The present invention relates generally to manufacture and repair of machine parts, and, more specifically, to surface finishing of such parts.
Machines are assemblies of various parts which are individually manufactured and assembled. Machines typically include metal parts, although synthetic and composite parts may also be used. And, each part requires specialized manufacturing.
For example, metal parts may be fabricated from metal stock in the form of sheets, plates, bars, and rods. Metal parts may also be formed by casting or forging. Such parts may be machined to shape in various manners.
Machining requires the selective removal of material to configure the part to its final shape and size within suitable manufacturing tolerances, typically expressed in mils, and with a suitable surface finish which is typically smooth or polished without blemish.
Each step in the manufacturing process of a given machine adds time and expense which should be minimized for producing a competitively priced product. It is desirable for each subsequent step in the manufacturing process to avoid damaging previously finished portions of the part which would then require additional corrective finishing steps.
Gas turbine engines are an example of a complex machine having many parts requiring precise manufacturing tolerances and fine surface finishes. A typical engine includes a multistage compressor for pressurizing air which is mixed with fuel in a combustor and ignited for generating hot combustion gases which flow downstream through one or more turbine stages that extract energy therefrom. A high pressure turbine powers the compressor, and a low pressure turbine provides output power, such as powering a fan disposed upstream from the compressor in an aircraft engine application.
The engine thusly includes various stationary components, and various rotating components which are typically formed of high strength, state of the art metal and composite materials. The various parts undergo several steps in their manufacturing and are relatively expensive to produce.
The various manufacturing processes result in various surface features which require additional processing for final acceptability. For example, sharp burrs must be removed; sharp corners must be radiused; and welding expulsion must be removed.
Hand grinding, grit blasting, and abrasive tumbling are just examples of typical post-processes used to finish the machined surfaces without damage thereto. However, these post-processes each require special equipment and add to the manufacturing time and cost.
A new process entitled Sustained Surface Scrubbing is being developed for quickly and efficiently removing burrs and expulsion and radiusing sharp corners at reduced cost. This basic process is described in U.S. Pat. No. 6,273,788 and is followed by several related patent applications including one recently issued as U.S. Pat. No. 6,183,347.
The various forms of Sustained Surface Scrubbing disclosed in these applications and patent include a pliant shot discharged in a carrier air stream at a shallow angle of incidence against a workpiece for the selective removal of material therefrom. The pliant shot is preferably a polyurethane cellular foam or sponge in small granular form and is preferably impregnated with different types of abrasive material as required for correspondingly different abrasive performance.
One form of the pliant shot is commercially available from Sponge-Jet Inc. of Eliot, Me. under the trademark of SPONGE-JET Media. This sponge media is formed with open cells for trapping contaminants during the intended blasting operations.
However, open-cell trapping of contaminants is undesirable in many applications wherein the pliant shot is intended to be reused for reducing costs. The open cell sponge media has limited strength and durability and affects the performance of the abrasive imbedded therein.
Accordingly, it is desired to provide an improved pliant shot for use in the several forms of Sustained Surface Scrubbing for increasing the strength and durability of the shot, and corresponding performance thereof.
A polymeric sponge includes cellulose fibers imbedded therein. The sponge is made by mixing water and cellulose fibers with a water-catalyzing prepolymer for chemical reaction thereof. The mixture is cured and granulated to size. The cellulose fibers enhance both the manufacturing process and the resulting sponge for increasing strength, durability, and performance thereof.